. >> reporter: they have limited choices, ron paul and mitt romney. >> and because they are the only ones who managed to get on the ballot. >> reporter: newt gingrich and rick santorum concentrated on earlier contests. romney got a boost on sunday from virginia's eric canter. >> he came out and agreed to endorse me which was great news. >> reporter: but helped santorum run as the political outsider. >> all of them have lined up behind the guy next in line with the most money. >> both santorum and romney held rallies in ohio, tuesday's big prize. >> if mitt romney can win ohio and he does well in places like georgia and tennessee and oklahoma, well, i think it will be tough to deny him the domination. >> reporter: but if santorum can do well in southern states and beat newt gingrich and georgia. >> then i think that he will be positioned to take us all the way to the convention. >> that is important to his continued candidacy. some virginia voters at that ron paul rally told them that they would like to see him leave a third party effort if he does not get the republican nomination. >